Organic electroluminescent element

ABSTRACT

Provided is a high-luminance, long-life laminated organic electroluminescent element. The organic electroluminescent element has a composition in which a plurality of light-emitting units, including at least one organic light-emitting layer, are laminated between a positive electrode and a negative electrode, and in which a linking layer is held between the respective light-emitting units. The linking layer is formed by laminating, in succession from the positive electrode side, an electron generating/transport section, an intermediate layer, and a hole generating/transport section, which contain at least one metal selected from a group consisting of an alkali metal, alkaline earth metal, rare earth metal, alloy of these metals, and compound of these metals. Preferably the intermediate layer contains an electrical insulating non-semiconductive substance having a specific resistance which is between 1.0×10 2  Ω·cm and 1.0×10 9  Ω·cm.

TECHNICAL FIELD

The present invention relates to an organic electroluminescent elementhaving plural organic light-emitting layers. Hereinafter, an organicelectroluminescent element may be referred to as an “organic ELelement”, or merely as an “element”.

BACKGROUND ART

Organic EL elements are semiconductor elements that convert electricalenergy to optical energy. In recent years, research using organic ELelements have been actively made, and the practical use thereof has beenadvancing. The organic materials constituting organic EL elements, andother aspects of organic EL elements have been improved, therebylowering the driving voltage of the elements remarkably and furtherenhancing the light-emitting efficiency thereof. In the market,televisions wherein an organic EL element is used as a display screenhave also been sold.

In order to make the luminance of an EL element higher, a high electricfield is applied to the element to make a current density high. However,by making the current density high, the quantity of generated heatincreases, causing a problem that deterioration of the organic thin filmitself is promoted. In order to solve this problem, it is necessary toraise the luminance of light emitted without changing the drivingcurrent.

In contrast, it has been recently reported (see, for example, PatentDocuments 1 to 3) that plural light-emitting layers for an organicelement are stacked on each other, and the layers are connected to eachother in series, thereby making it possible to make the luminance of theelement high. Patent Document 4 discloses a stacked-type organiclight-emitting element wherein an electrically insulatingcharge-generating layer containing a metal oxide such as vanadiumpentaoxide (V₂O₅) is arranged between plural organic light-emittingunits. Patent Document 5 suggests the use of a change-generating layerin which molybdenum trioxide is used instead of vanadium pentaoxide.

When an electric field is applied to such an organic light-emittingelement wherein a charge-generating layer is arranged betweenlight-emitting units, the charge-generating layer simultaneouslygenerates holes that can be injected into a hole-transporting layerarranged on the cathode side, and electrons that can be injected into anelectron-transporting layer arranged on the anode side. For this reason,the plural light-emitting units act like light-emitting units connectedto each other in series through the charge-generating layers. Such astacking method is called multi-photon emission (MPE).

For example, Patent Documents 3 and 4 disclose that a radicalanion-containing layer made of Alq:Liq/Al is used as an anode-side layerof such a charge-generating layer. In this structure, Li ions in Liq arereduced by a thermally reducing metal such as Al, and the resultant actsas a radical anion-generating means; thus; an electron-transportingorganic substance such as Alq is present in a radical anion state sothat electrons which can be injected into the electron-transportinglayer are generated.

In the structure where plural light-emitting units are connected to eachother, a layer arranged between the light-emitting units is variouslynamed. In the present specification, however, a region that issandwiched between plural light-emitting units in order to connect thetwo light-emitting units to each other is called a “connection layer”.For the structure of this “connection layer”, various forms aresuggested besides the structures disclosed in Patent Documents 3 and 4(see, for example, Patent Documents 5 to 7). When the connection layerhas a multi-layered structure, an extra voltage is generated in theconnecting region in accordance with the structure of the individuallayers or the stack order thereof. Thus, this voltage may causeinconveniences such as that the connection layer becomes unstable, andthat reliability for long lifetime cannot be obtained.

For example, when vanadium oxide is arranged on the anode side of acharge-generating layer, stoichiometry of the material thereof isimportant. If its composition ratio departs therefrom, thecharge-generating layer becomes unstable. The unstable charge-generatinglayer reduces the function thereof remarkably. In order to enable aconnection layer to act stably as a charge-generating layer, it is knownthat an interfacial structure on the anode-side of the connection layeris very important.

In the meantime, Patent Document 7 discloses that a layer made of anoxide of an alkali metal or alkaline earth metal is arranged on theanode side of a connection layer. In this oxide layer, metal ions of theoxide act as an electron-donating dopant, so that this layer has aneffect of improving the efficiency of injecting electrons to thelight-emitting unit present on the anode side of the connection layer.However, when a metal oxide such as lithium carbonate (Li₂CO₃) isproduced, metal ions easily diffuse to the organic layer. As a result,it is feared that the lifetime of the element is made short.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: JP-B-11-329748-   Patent Document 2: JP-B-2003-45676-   Patent Document 3: JP-B-2003-264085-   Patent Document 4: JP-A-2003-272860-   Patent Document 5: JP-A-2006-24791-   Patent Document 6: JP-A-2008-532229-   Patent Document 7: JP-A-2006-351398

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In light of the above-mentioned matter, an object of the invention is toprovide an organic EL element including plural light-emitting unitslaminated over each other wherein the structure of a connection layer orconnection layers arranged between the units is improved to give anexcellent reliability.

Means for Solving the Problems

In order to solve the problems, the inventors have made eagerinvestigations, and they have found out that, according to a structuredescribed below, an organic EL element structure excellent inreliability can be provided. Thus, the invention has been completed.

The invention relates to an organic electroluminescent element whereinplural light-emitting units 3 each comprising at least one organiclight-emitting layer are stacked between an anode 2 and a cathode 5, anda connection layer 4 is sandwiched between the respective light-emittingunits. In the connection layer 4-1, the following are successivelystacked from the anode 2 side: an electron-generating and transportingsection 4-1-a; an intermediate layer 4-1-b; and a hole-generating andtransporting section 4-1-c.

The electron-generating and transporting section 4-1-a comprises atleast one selected from the group consisting of alkali metals, alkalineearth metals, rare earth metals, and alloys and compounds of thesemetals. Among these, in the electron-generating and transportingsection, lithium compounds are preferably used, and LiF is mostpreferably used. The hole-generating and transporting section 4-1-cpreferably comprises an azatriphenylene derivative, or a metal oxidehaving a hole-injecting ability. The metal oxide having a hole-injectingability may be molybdenum oxide, ruthenium oxide, manganese oxide,tungsten oxide, vanadium oxide or some other, and is preferablymolybdenum trioxide.

In a first embodiment of the invention, the intermediate layer 4-1-b isa layer comprising a non-semiconductor substance which is electricallyinsulating. The electrically insulating non-semiconductor substancepreferably has a resistivity of 1.0×10² to 1.0×10⁹ Ω·cm. Theelectrically insulating non-semiconductor substance preferably has adielectric constant of 2 to 4.5 inclusive.

In a second embodiment of the invention, the intermediate layer 4-1-b isa layer comprising a charge-transporting organic material. Examples ofthe charge-transporting organic material include electron-transportingmaterials, hole-transporting materials, and ambipolar-transportingmaterials.

Furthermore, the invention relates to a display device and a lightingapparatus each comprising the above-mentioned organic electroluminescentelement.

Effects of the Invention

Since the organic EL element of the invention has the intermediate layer4-1-b between the electron-generating and transporting section 4-1-a andthe hole-generating and transporting section 4-1-c of the connectionlayer 4-1, interaction between the electron-generating and transportingsection and the hole-generating and transporting section is restrained.For this reason, even in the case of using, for the electron-generatingand transporting section 4-1-a, lithium fluoride or any other substanceexhibiting a strong interaction with a hole-generating and transportingmaterial, the connection layer 4 functions as a charge-generating layer.According to this structure, the luminance of the element can berestrained from being deteriorated, and further the extension of thelifetime and an improvement in the reliability can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating a structure of an organic ELelement of an embodiment of the invention.

FIG. 2 is a graph showing the voltage-to-current densities of ReferenceExamples 1 and 2.

FIG. 3 is a graph showing the voltage-to-current densities of ReferenceExamples 1 and 3.

FIG. 4 is a graph showing the voltage-to-current densities of ReferenceExamples 1 and 4.

FIG. 5 are each a graph showing a characteristic of each element ofExample 1 and Reference Example 5. FIG. 5(1), FIG. 5(2) and FIG. 5(3)show a voltage-to-current density, a light-emitting efficiency, and acurrent efficiency thereof, respectively.

FIG. 6 are each showing a characteristic of each element of Example 2and Reference Example 6. FIG. 6(1), FIG. 6(2) and FIG. 6(3) show avoltage-to-current density, a light-emitting efficiency, and a currentefficiency, respectively.

FIG. 7 is a graph showing the voltage-to-current densities of Example 2and Comparative Example 3.

FIG. 8 is a graph showing the voltage-to-current densities of Examples2, 3-1, 3-4 and 3-5.

FIG. 9 is a graph showing the voltage-to-current densities of Examples2, and 3-1 to 3-5 in the range of high voltages.

FIG. 10 are each a graph showing a characteristic of each element ofExample 3-4 and Reference Example 6. FIG. 10(1), FIG. 10(2) and FIG.10(3) show a voltage-to-current density, a light-emitting efficiency,and a current efficiency, respectively.

FIG. 11 are each a graph showing a characteristic of each element ofComparative Example 3 and Reference Example 6. FIG. 11(1), and FIG.11(2) show a voltage-to-current density and a light-emitting efficiency,respectively.

FIG. 12 is a graph showing the voltage-to-current densities of Example3-4, Comparative Example 3, and Reference Example 6.

FIG. 13 is a graph showing the voltage-to-current densities of Example 4and Reference Example 6.

FIG. 14 is a graph showing lifetime test results of Example 1,Comparative Example 1, and Reference Example 5.

FIG. 15 is a graph showing lifetime test results of Example 2,Comparative Example 3, and Reference Example 6.

FIG. 16 are each a graph showing a characteristic of each element ofExample 5, Comparative Example 4 and Reference Example 7. FIG. 16(1) andFIG. 16(2) show a voltage-to-current density, and a light-emittingefficiency, respectively.

FIG. 17 are each a graph showing a characteristic of each element ofExample 6, Comparative Example 5 and Reference Example 8. FIG. 17(1) andFIG. 17(2) show a voltage-to-current density, and a light-emittingefficiency, respectively.

FIG. 18 is a graph showing lifetime test results of Examples 9 and 10,Comparative Example 8 and Reference Example 10.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments according to the invention will be described indetail with reference to the drawings. FIG. 1 schematically illustratesa cross section structure of an organic EL element according to anembodiment of the invention. The element illustrated in this figure hasa substrate 1, an anode 2, plural light-emitting units 3-1 and 3-2 thatare successively stacked over the anode 2, a connection layer 4-1provided between the light-emitting units, and a cathode 5 stacked onthe light-emitting unit 3-2. In FIG. 1, a structure having twolight-emitting units is illustrated; however, the element of theinvention may have a structure having three or more light-emittingunits. In the structure having three or more light-emitting units, it ispreferred to provide a connection layer between any adjacent two of thelight-emitting units.

The substrate 1 provided in the organic EL element is not particularlylimited, and may be a known substrate. The substrate 1 may beappropriately selected from, for example, transparent substrates such asa glass piece; a silicon substrate; and flexible film substrates. In thecase of a bottom emission type organic EL element in which light istaken out from the substrate side, the transmittance of the substrate 1is preferably 80% or more in the range of visible rays, more preferably95% or more from the view point of reducing a loss of emitted light.

The anode 2 provided on the substrate 1 is not particularly limitedeither, and may be a known anode. Examples thereof include indium tinoxide (ITO), indium zinc oxide (IZO), SnO₂, and ZnO. Of these examples,ITO or IZO, which are high in transparency, is preferred from theviewpoint of the efficiency of taking out light generated from thelight-emitting layer, and ease of patterning. The anode may beoptionally doped with one or more dopants such as aluminum, gallium,silicon, boron, niobium and the like.

From the viewpoint of transparency, the transmittance of the anode 2 ispreferably 70% or more, more preferably 80% or more, in particularpreferably 90% or more in the range of visible rays. The method forforming the anode 2 on the substrate 1 is not particularly limited, andmay be, for example, sputtering or thermal CVD.

The following describes the light-emitting units 3. Each of thelight-emitting units 3 corresponds to constituting-elements of theremainder obtained by excluding both an anode and a cathode fromconstituting-elements of a conventional organic EL element having asingle light-emitting unit. Each of the light-emitting units has atleast one light-emitting layer substantially made of an organiccompound. Each of the light-emitting units 3 may have any stackedstructure as far as the unit has at least one light-emitting layer. Theunit may have, for example, a structure having a hole-injecting layer ora hole-transporting layer, or some other on the anode side of thelight-emitting layer, and further having an electron-transporting layeror an electron-injecting layer or some other on the cathode side of thelight-emitting layer.

The method for forming individual layers that constitute each of thelight-emitting units 3 is not particularly limited. A part of theorganic layers may be formed by, for example, a spin coating methodbesides vacuum deposition. Materials used in the hole-injecting layer,the hole-transporting layer, the light-emitting layer, theelectron-transporting layer, the electron-injecting layer, and otherlayers are not particularly limited either, and may each be anyappropriate known substance. Furthermore, organic materials used in thelight-emitting layer are not particularly limited either, and may be anyknown substance.

It is preferred that each of the light-emitting units has ahole-transporting layer on the anode side thereof. It is particularlypreferred that the light-emitting unit 3-2 arranged on the cathode sideof the connection layer 4-1, which will be described later, has ahole-transporting layer containing an arylamine compound. In this case,the arylamine compound is easily converted into a radical cation,thereby raising the efficiency of transporting holes from ahole-generating and transporting section 4-1-c to the light-emittinglayer of the light-emitting unit 3-2.

Examples of the arylamine compound used in the hole-transporting layerinclude N,N,N′,N′-tetraphenyl-4,4′-diaminophenyl,N,N′-diphenyl-N,N′-di(3-methylphenyl)-4,4′-diaminobiphenyl,2,2-bis(4-di-p-tolylaminophenyl)propane,N,N,N′,N′-tetra-p-tolyl-4,4′-diaminobiphenyl,bis(4-di-p-tolylaminophenyl)phenylmethane,N,N′-diphenyl-N,N′-di(4-methoxyphenyl)-4,4′-diaminobiphenyl,N,N,N′,N′-tetraphenyl-4,4′-diaminodiphenyl ether,4,4′-bis(diphenylamino)quadriphenyl,4-N,N′-diphenylamino-(2-diphenylvinyl)benzene,3-methoxy-4′-N,N-diphenylaminostilbene, N-phenylcarbazole,1,1-bis(4-di-p-triaminophenyl)-cyclohexane,1,1-bis(4-di-p-triphenyl)cyclohexane,1,1-bis(4-di-p-triaminophenyl)-4-phenylcyclohexane,bis(4-dimethylamino-2-methylphenyl)-phenylmethane,N,N,N—N-tri(p-tolyl)amine,4-(di-p-tolylamino)-4′-[4(di-p-triamino)styryl]stilbene,N,N,N′,N′-tetraphenyl-4,4′-diamino-biphenyl-N-phenylcarbazole,4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl,4,4′-bis[N-(1-naphthyl)-N-phenylamino]p-terphenyl,4,4′-bis[N-(3-acenaphthenyl)-N-phenyl-amino]biphenyl,1,5-bis[N-(1-naphthyl)-N-phenyl-amino]naphthalene,4,4′-bis[N-(9-anthorine)-N-phenyl-amino]biphenyl,4,4′-bis[N-(1-anthryl)-N-phenyl-amino]p-terphenyl,4,4′-bis[N-(2-phenanthryl)-N-phenyl-amino]biphenyl,4,4′-bis[N-(8-fluoranthenyl)-N-phenyl-amino]biphenyl,4,4′-bis[N-(2-pyrenyl)-N-phenylamino]biphenyl,4,4′-bis[N-(2-perylenyl)-N-phenyl-amino]biphenyl,4,4′-bis[N-(1-coronenyl)-N-phenyl-amino]biphenyl,2,6-bis[di-(1-naphthyl)amino]naphthalene,2,6-bis[N-(1-naphthyl)-N-(2-naphthyl)amino]naphthalene,4,4′-bis[N,N-di(2-naphthyl)amino]terphenyl,4,4′-bis{N-phenyl-N-[4-(1-naphthyl)phenyl]amino}biphenyl,4,4′-bis[N-phenyl-N-(2-pyrenyl)-amino]biphenyl,2,6-bis[N,N-di(2-naphthyl)amino]fluorene,4,4′-bis[N-phenyl-N-(2-pyrenyl)-amino]biphenyl,2,6-bis[N,N-di-p-triamino]terphenyl,bis(N-1-naphthyl)(N-2-naphthyl)amine, and4,4′-bis[N-(2-naphthyl)-N-phenyl-amino]biphenyl. Additionally, knownsubstances used in organic EL elements may be used.

It is preferred that the hole-transporting layer contains, as thearylamine compound, a triarylamine derivative. It is particularlypreferred that the layer contains4,4′-bis[N-(2-naphthyl)-N-phenyl-amino]biphenyl (also referred to as“α-NPD” or “NPB”), which is represented by the following chemicalformula:

The following describes the cathode 5. Materials used in the cathode 5are preferably a metal having a low work function, any alloy thereof,any metal oxide thereof, or some other. Examples of the metal having alow work function include Li as an alkali metal, and Mg and Ca asalkaline earth metals. A metallic simple substance made of a rare earthmetal or some other; an alloy of these metals and Al, In, Ag or someother; or the like may also be used. As disclosed in JP-A-2001-102175and others, an organic metal complex compound containing at least oneselected from the group consisting of alkaline earth metal ions andalkali metal ions may be used for an organic layer contacting thecathode. In this case, it is preferred to use, for the cathode, a metalcapable of reducing the metal ion of the complex compound into a metalin a vacuum, for example, Al, Zr, Ti or Si, or an alloy containing thesemetals.

The following describes the structure of the connection layer 4, whichis a feature of the invention. Each connection layer 4 is sandwichedbetween two light-emitting units. For example, in FIG. 1, the connectionlayer 4-1 is sandwiched between the light-emitting units 3-1 and 3-2. Ina specific embodiment, the connection layer 4 has a structure whereinfrom the anode 2 side, an electron-generating and transporting section4-1-a, an intermediate layer 4-1-b, and a hole-generating andtransporting section 4-1-c are successively stacked. In the firstembodiment of the invention, the intermediate layer 4-1-b is a layercontaining a non-semiconductor substance which is electricallyinsulating. In the second embodiment of the invention, the intermediatelayer 4-1-b is a layer containing a charge-transporting organicmaterial.

First, a description is made about an embodiment of the connection layerin the first embodiment. In the electron-generating and transportingsection 4-1-a, the process by which electron-transporting molecules makea transition from electrically neutral molecules into a radical anionstate is repeatedly performed, thereby generating electrons andtransporting the electrons to the first light-emitting unit 3-1 adjacentto the anode 2 side. The electron-generating and transporting section4-1-a preferably contains an electron-donating metal such as an alkalimetal, an alkaline earth metal or a rare earth metal, or a compound ofthese metals (these may be correctively referred to as an “alkali metalor the like” hereinafter). Preferably, the alkali metal is Li or someother, the alkaline earth metal is Mg, Ca or some other, and the rareearth metal is Eu, Ce or some other. An alloy of such a metal and Al,Ag, In or some other is also preferably used. Of these examples, alkalimetals are preferred, and Li is particularly preferred.

The alkali metal or the like may be present in the form of an inorganicmetal compound (provided that any metal oxide is excluded) such aslithium fluoride (LiF), or an organic metal compound such as(8-quinolinolato) lithium complex (Liq). Among these, lithium fluorideis suitable for extending the lifetime of the organic EL element sincelithium fluoride does not easily diffuse into the light-emitting unit3-1.

LiF is excellent in efficiency of injecting electrons from the cathodeto the light-emitting unit, and is effective for lowering the drivingvoltage of the organic EL element. Thus, in conventional organic ELelements, LiF is widely used for a buffer layer for their cathode.However, reports have hardly been made about examples where LiF is usedfor connection layers of an MPE type element in which plurallight-emitting units are stacked. It is assumed that this matter iscaused by a difference in structure between the cathode and theconnection layers.

That is, when LiF is used for the electron-generating and transportingsection arranged on the anode side of the connection layer, LiF isarranged adjacently to or in the vicinity of the hole-generating andtransporting section arranged on the cathode side of the connectionlayer to act as a charge-generating layer. However, an interaction isstrong between the electron-generating and transporting section 4-1-ausing LiF and the hole-generating and transporting section 4-1-c; thus,electrons generated in the electron-generating and transporting section4-1-a and holes generated in the hole-generating and transportingsection 4-1-c are not transported into the light-emitting unit 3-1 orthe light-emitting unit 3-2 so that the electrons and the holes easilyremain the connection layer 4-1. By the effect of such an interaction,an electric current does not easily flow in the element. Therefore, inorder to gain a desired luminance, it is necessary to cause an excessiveelectric current to flow in the element. As a result, the lifetime ofthe element tends to become short. It is considered that in order toavoid such a problem, LiF, which is strong in interaction with thehole-generating and transporting section, has not been hitherto used foran electron-generating and transporting section of the connection layer.

For example, Patent Document 7 (JP-A-2006-351398) described abovediscloses a connection layer having a charge-transporting material layerincluding Alq₃ or some other between a layer containing an oxide such asLi₂CO₃ as an electron-injecting layer and an azatriphenylene derivativeas a hole-generating layer. It is mentioned that according to thisstructure, deterioration based on interaction between theelectron-injecting layer and the hole-generating layer is restrained. Onthe other hand, JP-A-2006-351398 states that when LiF is used for theelectron-injecting layer, increase in voltage and deterioration inluminance are observed.

In contrast, in the first embodiment of the invention, a layercontaining an electrically insulating non-semiconductor substance isarranged, as an intermediate layer 4-1-b between the electron-generatingand transporting section 4-1-a and the hole-generating and transportingsection 4-1-c, which will be described later. For this reason, even whenLiF is used for the electron-generating and transporting section 4-1-a,the interaction thereof with the hole-generating and transportingsection 4-1-c is restrained so that the high electron-injectingefficiency that LiF has is maintained. Thus, the driving voltage can bemade low, and lifetime can be extended.

The inventors have actually produced MPE type elements each having aconnection layer having a stacked structure of Li₂CO₃/Alq₃/anazatriphenylene derivative, as disclosed in JP-A-2006-351398, and thenevaluated the element. As a result, the inventors have found out thatbetween elements having the same structure among these elements,characteristics are varied. It is assumed that this matter is caused byan instable connection between the oxide such as Li₂CO₃, and theazatriphenylene derivative. In contrast, in the first embodiment of theinvention, wherein the intermediate layer 4-1-b contains theelectrically insulating non-semiconductor substance, a variation incharacteristics is small between the elements having the same structure.Thus, a stable connecting state can be generated between theelectron-generating and transporting section 4-1-a and thehole-generating and transporting section 4-1-c.

The electron-generating and transporting section 4-1-a may be, besidesthe layer of a simple substance of an alkali metal or the like, forexample, a mixed layer of an alkali metal or the like and an organiccompound such as an electron-transporting material. Such a mixed layermay be formed by, for example, vapor co-deposition. In the mixed layer,the ratio by volume of the organic compound to the alkali metal or thelike is preferably from 0.1 to 10. The organic compound that is combinedwith the alkali metal or the like to form the mixed layer is preferablytris(8-hydroxyquinolinato) aluminum (III) (Alq₃), which is anelectron-transporting material.

The electron-generating and transporting section 4-1-a preferably has,on the cathode side thereof, a layer made of a thermally reducing metalcapable of reducing an alkali metal ion, an alkaline earth metal ion ora rare earth metal ion of the electron-generating and transportingsection to a metal in a vacuum, an example of the thermally reducingmetal being Al, Zr, Ti or Si, or an alloy containing these metals. Asdescribed in JP-A-2000-182774, the thermally reducing metal makes itpossible to reduce and isolate a metal in a metal compound by reducingreaction in a vacuum, and acts as a “reducing reaction generating layer”for the electron-generating and transporting section. The element hasthe reducing reaction generating layer, thereby reducing the metal ionin the electron-generating and transporting section effectively. Thus, abarrier against injection of electrons from the electron-generating andtransporting section 4-1-a to the anode-side light-emitting unit 3-1becomes small so that the driving voltage of the element can be lowered.The reducing reaction generating layer also has an effect of restrainingthe diffusion of the metal ion in the electron-generating andtransporting section 4-1-a. The thermally reducing metal for forming thereducing reaction generating layer is in particular preferably Al, andthe film thickness thereof is preferably 5 nm or less, more preferably 2nm or less.

The following describes the layer 4-1-b, which contains an electricallyinsulating non-semiconductor substance, in the connection layer 4. Thenon-semiconductor substance used in the layer 4-1-b is not particularlylimited as far as the substance has an electrically insulating propertyand exhibits no property of a semiconductor. The resistivity thereof ispreferably 1.0×10²Ω·cm or more, more preferably 1.0×10⁵ Ω·cm or more.The dielectric constant of the non-semiconductor substance is preferably4.5 or less, more preferably 4 or less. If the resistivity is too low orthe dielectric constant is too high, the effect of restraining theinteraction between the electron-generating and transporting section andthe hole-generating and transporting section is not sufficientlyobtained; thus, the element tends to be easily deteriorated by theremaining charges in the connection layer or by an increase in drivingvoltage that is associated with the remaining charges.

The intermediate 4-1-b contains the non-semiconductor substance, whichhas an electric insulating property (resistivity) and a dielectricconstant as described above, thereby restraining the interaction betweenthe electron-generating and transporting section 4-1-a and thehole-generating and transporting section 4-1-c. This matter contributesto a fall in the driving voltage or an extension of the lifetime of theelement. Moreover, the intermediate layer 4-1-b is electricallyinsulating, so that an advantage can be obtained that the anode made ofITO or some other and the intermediate layer can easily be electricallyinsulated to each other by a mask vapor deposition or some other method.

By contrast, if the resistivity of the non-semiconductor substance istoo high, charges tend to remain easily in the connection layer. Fromthis viewpoint, the resistivity of the non-semiconductor substance ispreferably 1.0×10⁹ Ω·cm or less, more preferably 1.0×10⁸ Ω·cm or less.If the dielectric constant of the non-semiconductor substance is toolow, an amorphous film tends not to be easily formed by vacuumdeposition. From this viewpoint, the dielectric constant of thenon-semiconductor substance is preferably 2 or more, more preferably 2.5or more.

The resistivity and the dielectric constant can each be calculated outfrom a current response to application of a voltage. The dielectricconstant may be measured by analyzing a measurement cell in which atarget sample having a predetermined thickness is sandwiched between anITO electrode layer (150 nm) and an Al electrode layer (100 nm) throughimpedance spectrometry using an electrochemical analysis apparatus (forexample, model 660B, manufactured by BAS Inc.). First, in anAC-impedance mode, an equivalent circuit of the cell is presumed from atrace of the impedance Z on a complex plane. Next, in animpedance-potential mode, an electrostatic capacity is calculated fromthe equivalent circuit that is presumed to be a potential waveform ofthe impedance-potential. The dielectric constant is then decided. Thedielectric constant may depend on a film thickness; in this case,however, it is advisable to adopt, as the dielectric constant of thesubstance, a value of the substance that is of 100 nm thickness.

The intermediate layer 4-1-b is preferably formed by vacuum depositionsince this method makes it possible to control the film thicknesseasily. The non-semiconductor substance used in the intermediate layeris preferably a compound that can be formed into a film by vacuumdeposition. Preferred examples of the compound include organic metalcomplexes such as bis(2,2,6,6-tetramethyl-3,5-heptanedionato)calcium(another name: bis(dipivaloylmethanato)calcium, which may be abbreviatedto Ca(DPM)₂), bis(2,4-pentanedionato)magnesium (another name:bis(acetylacetonate)magnesium, which may be abbreviated to Mg(acac)₂),bis(2,2,6,6-tetramethyl-3,5-heptanedionato)magnesium (another name:bis(dipivaloylmethanato)magnesium, which may be abbreviated toMg(DPM)₂), 2,2,6,6-tetramethyl-3,5-heptanedionatolithium (another name:dipivaloylmethanato lithium, which may be abbreviated to Li(DPM)),tris(2,2,6,6-tetramethyl-3,5-heptanedionato)aluminum (another name:tris(dipivaloylmethanato)aluminum, which may be abbreviated toAl(DPM)₃).

The non-semiconductor substance used in the non-semiconductor substancecontaining layer 4-1-b in the connection layer 4 should be preferablyexcellent in optical transparency and be excellent in transmissivity inthe range of visible rays. When the non-semiconductor substancecontaining layer 4-1-b is a single layer made of an electricallyinsulating non-semiconductor substance, the film thickness thereof ispreferably from 2 to 10 nm. When the thickness of the non-semiconductorsubstance containing layer is too thin, the interaction between theelectron-generating and transporting section 4-1-a and thehole-generating and transporting section 4-1-c is not effectivelyrestrained so that the driving voltage of the element may rise.Conversely, if the thickness of the non-semiconductor substancecontaining layer is too thick, a tunnel probability between theelectron-generating and transporting section 4-1-a and thehole-generating and transporting section 4-1-c falls largely so that nocharges are shifted. Thus, the connection layer 4 tends not to act as acharge-generating layer. From this viewpoint, when the layer 4-1-b is asingle layer made of an electrically insulating non-semiconductorsubstance, the film thickness thereof is preferably 8 nm or less, morepreferably 3 nm or less.

The intermediate layer 4-1-b may be, besides a single layer of anelectrically insulating non-semiconductor substance, for example, amixed layer with an electrically insulating non-semiconductor substanceand a hole-generating and transporting material. In order to make thedriving voltage of the MPE type element low, the content of theelectrically insulating non-semiconductor substance in this mixed layeris preferably 10% or more by weight, more preferably 25% or more byweight. The hole-generating and transporting material in the mixed layeris preferably an azatriphenylene derivative used in the hole-generatingand transporting section 4-1-c, which will be described later, or ametal oxide having a hole-injecting ability.

When the intermediate layer 4-1-b is rendered as a mixed layer, thedegree of freedom for optical adjustment of the MPE type element can beimproved. In the MPE type element, in order to optimize the efficiencyof taking out light from each of the light-emitting unit layers, it ispreferred to adjust an optical path length. For example, in the elementin FIG. 1, in the case of taking out light from the substrate 1 side, itis preferred to optimize not only the optical path length from thelight-emitting layer of the first light-emitting unit 3-1 to alight-taking-out point but also that from the light-emitting layer ofthe second light-emitting unit 3-2 to a light-taking-out point. When theoptical path length from the light-emitting layer of the firstlight-emitting unit 3-1 is optimized by adjusting the thickness of theanode 2 or by some other way, the film thickness of the intermediatelayer 4-1-b may be required to be adjusted in order to also optimize theoptical path length from the light-emitting layer of the secondlight-emitting unit 3-2. However, when the intermediate layer 4-1-b is asingle layer of an electrically insulating non-semiconductor substance,an adjustable range of the film thickness may be restricted as describedabove; thus, the optical path length is not optimized so that theefficiency of taking out light from the second light-emitting unit layermay be required to be sacrificed. In contrast, when the intermediatelayer 4-1-b is rendered a mixed layer with the substance and ahole-generating and transporting material, the tunnel probabilitybecomes higher than compared to a single layer of an electricallyinsulating non-semiconductor substance even when these layers have thesame thickness. Thus, even when the thickness of the intermediate layeris, for example, more than 10 nm, the connection layer 4 can keep thefunction as a charge-generating layer; therefore, the optical pathlength can be adjusted to optimize the efficiency of taking out lightfrom the second light-emitting unit. When the intermediate layer 4-1-bis the mixed layer, the thickness thereof is not particularly limited. Avalue obtained by multiplying the content (percentage by weight) of theelectrically insulating non-semiconductor substance by the thickness ispreferably from 2 to 10 nm, more preferably from 2 to 8 nm, even morepreferably from 2 to 3 nm.

When the intermediate layer 4-1-b is the mixed layer and a metal oxidehaving a hole-injecting ability is used for the hole-generating andtransporting section 4-1-c, which will be described below, theintermediate layer 4-1-b is preferably a mixed layer of an electricallyinsulating non-semiconductor substance and molybdenum trioxide. In thiscase, it is preferred that the content of the electrically insulatingnon-semiconductor substance is 10% or more by weight and the content ofmolybdenum trioxide is 10% or more by weight.

The following describes the hole-generating and transporting section4-1-c in the connection layer 4. The hole-generating and transportingsection may be any section having a function of generating holes andtransporting the holes. In an embodiment, the hole-generating andtransporting section preferably contains an azatriphenylene derivativerepresented by the following general formula:

wherein R1 to R6 are each independently selected from a group consistingof hydrogen, nitrile, nitro, sulfonyl, sulfoxides, trifluoromethyl,esters, amides, substituted or unsubstituted aryls, substituted orunsubstituted heteroaryls, and substituted or unsubstituted alkyls; andany adjacent Rn's wherein n represents 1 to 6 may be bonded to eachother through a cyclic structure.

The azatriphenylene derivative which has an electron-withdrawingproperty is stacked on or mixed with a material having ahole-transporting property in order to be brought into contact with eachother, whereby this charged material which has a hole-transportingproperty is easily converted into a radical cation form. For thisreason, when the light-emitting unit 3-2 adjacent to the hole-generatingand transporting section 4-1-c contains, for the hole-transportinglayer, a material having an electron-donating property like theabove-mentioned arylamine compound, the electron-donating compound whichconstitutes the hole-transporting layer is easily converted into aradical cation form so that the performance of transporting holes fromthe connection layer 4 to the light-emitting unit 3-2 is improved.

In another embodiment, the hole-generating and transporting section4-1-c preferably contains a metal oxide having a hole-injecting ability.In this case, the hole-generating and transporting section 4-1-c may bea single layer made of the metal oxide having a hole-injecting ability,or may be a mixed layer of the oxide and a hole-transporting materialsuch as an arylamine compound.

Examples of the metal oxide having a hole-injecting ability includevanadium oxide (V₂O₅ or VO₅), ruthenium oxide (RuO₄ or RuO₂), manganeseoxide (MnO or MnO₂), or molybdenum oxide (MoO₂ or MoO₃). As described inJP-A-2006-24791, a metal oxide such as molybdenum trioxide is stackedover or mixed with a charged material having a hole-transportingproperty to be brought into contact each other, thereby forming a chargetransfer complex, so that the charged material having ahole-transporting property is converted into a radical cation form.Herein, the charge transfer complex is any compound having a chargetransfer interaction among intermolecular compounds each formed ofmolecules of two or more kinds. From molybdenum trioxide, which is anelectron-donating molecule, charges are partially transferred to anelectron-accepting molecule that is the hole-transporting material, sothat the charged molecules form a complex by an attractive force such asorbital interaction, electrostatic interaction or some other. Thus, whenthe second light-emitting unit 3-2 adjacent to the hole-generating andtransporting section 4-1-c contains, for the hole-transporting layer, anelectron-donating material like the above-mentioned arylamine compound,the electron-donating compound which constitutes the hole-transportinglayer is easily converted into a radical cation form. As a result, theperformance of transporting holes from the connection layer 4 to thesecond light-emitting unit 3-2 is improved.

In the connection layer 4, the hole-generating and transporting section4-1-c may function also as a hole-injecting layer constituting a partialregion of the second light-emitting unit 3-2 adjacent to the cathodeside of the connection layer 4. In this case, it is not necessarilyessential to provide a hole-injecting layer into the light-emitting unit3-2.

The connection layer 4-1 described above acts as a charge-generatinglayer which fulfills a function of injecting holes toward a cathodedirection and injecting electrons toward an anode direction. In thefirst embodiment of the invention, the intermediate layer 4-1-b of theconnection layer has the electrically insulating non-semiconductorsubstance; therefore, even when a non-oxide such as LiF is used for theelectron-generating and transporting section 4-1-a, the element isrestrained from being deteriorated by the interaction with thehole-generating and transporting section 4-1-c. Thus, the lifetime ofthe element is improved. Additionally, LiF has lower levels of diffusionto any organic layer than metal oxides such as Li₂CO₃, and is furtherexcellent in electron-injecting efficiency, so that LiF is effective forlowering the driving voltage of the organic EL element.

The following describes the second embodiment of the invention wherein alayer containing a charge-transporting organic material is used as theintermediate layer 4-1-b. The second embodiment is similar to the firstembodiment except that the layer which contains a charge-transportingorganic material is used instead of the layer containing theelectrically insulating non-semiconductor substance in the firstembodiment. The “charge-transporting organic material” means an organiccompound in which electrons or holes having charges for electricresistance or thermal electromotive force can be shifted in a substance.

In the second embodiment, the layer 4-1-b containing thecharge-transporting organic material may be a single layer of acharge-transporting organic material, or a mixed layer of acharge-transporting organic material and a hole-generating andtransporting material. Examples of the mixed layer include, morespecifically, a mixed layer of a charge-transporting organic materialand an azatriphenylene derivative, or a mixed layer of acharge-transporting organic material and a metal oxide having ahole-injecting ability.

In order to restrain a rise in the voltage of the element, the contentof the charge-transporting organic material in this mixed layer ispreferably 20% or more by weight, more preferably 30% or more by weight.

Examples of an electron-transporting material which is an example of thecharge-transporting organic material include Bathocuproin (BCP), andtris(8-hydroxyquinolinato)aluminum (III) (Alq₃). Of these examples, Alq₃is preferably used from the viewpoint of versatility. Examples of ahole-transporting material which is an example of thecharge-transporting organic material include arylamine compounds. Ofthese examples, α-NPD is preferably used from the viewpoint of a highversatility. It is allowable to use a compound having an ambipolartransporting property such as 4,4′-bis(N-carbazolyl)biphenyl (CBP) whichis represented by the following chemical formula:

The film thickness of the “layer containing a charge-transportingorganic material” is preferably from 20 to 100 nm inclusive, morepreferably from 50 to 100 nm inclusive in order to restrain a rise inthe voltage of the element.

As described above, according to the invention, in an organic EL elementwherein plural light-emitting units are stacked, a connection layer orconnection layers (each) having an intermediate layer 4-1-b is/are usedbetween the light-emitting units, thereby restraining interactionbetween the electron-generating and transporting section 4-1-a and thehole-generating and transporting section 4-1-c, so that the elementhaving a low level in initial-luminance deterioration and a longlifetime can be obtained. In the case of using, in particular, lithiumfluoride for the electron-generating and transporting section 4-1-a, itis possible to attain a drop in driving voltage as well as the longlifetime.

When the organic EL element of the invention is made into a structurewherein respective light-emitting units 3 have different luminouscolors, desired mixed color emission can be obtained. When respectivepixels are divided into three primary colors of R, G and B, for example,in a manner of using a shadow mask or some other manner, a color displayelement can be produced. The organic EL element is a spontaneouslylight-emitting device; thus, the element does not require any backlightor the like so that the element can be made super-thin for the use of adisplay. Additionally, the element is also low in consumption power, sothat the element can be effectively applied to a lighting apparatus aswell as a display device from the viewpoint of energy saving.

EXAMPLES

Next, a description is made about processes for producing organic ELelements of specific Examples of the invention and Comparative Examplesagainst these Examples, and evaluation results thereof.

Reference Examples 1 to 4

In order to check operation of respective connection layers of theinvention, the structure of the connection layer of the invention andthe structure of a connection layer of each of the Comparative Exampleswere each arranged on the cathode side of an organic-EL-element having asingle light-emitting unit. A current-voltage measurement was thenconducted. In each of Reference Examples 1 to 4, described below, abottom-type evaluation substrate was produced that had a light-emittingregion 2 mm×2 mm in size formed on a glass substrate on which apatterned ITO film (thickness: 150 nm) was formed as an anode.

Reference Example 1

The following was formed into a film of 10 nm thickness as ahole-injecting layer on the ITO anode by vacuum deposition (depositionrate: 0.5 to 0.8 nm/sec): a hole-injecting compound made of atriphenylene derivative represented by the following chemical formula(hereinafter abbreviated to HAT(CN)₆):

Next, the following was formed into a film of 50 nm thickness as ahole-transporting layer by vacuum deposition (deposition rate: 0.8 to1.2 nm/sec): 4,4′-bis[N-(2-naphthyl)-N-phenyl-amino]biphenyl(hereinafter abbreviated to α-NPD) represented by the following chemicalformula:

Next, the following was formed into a film of 60 nm thickness as alight-emitting layer by vacuum deposition (deposition rate: 2.9 to 3.1nm/sec): [tris(8-hydroxyqunolinato)]aluminum (III) (hereinafterabbreviated to Alq₃) represented by the following chemical formula:

On the light-emitting layer an electron-generating and transportingsection 4-1-a, an intermediate layer 4-1-b, and a hole-generating andtransporting section 4-1-c were successively formed. First, LiF wasformed into a film of 1 nm thickness as the electron-generating andtransporting section 4-1-a, and then Al was formed into a film of 1 nmthickness as a layer for generating a reducing reaction with the LiFlayer. The following was then formed into a film of 3 nm thickness, asthe non-semiconductor substance containing layer 4-1-b, thereon(deposition rate: 0.5 nm/sec):bis(2,2,6,6-tetramethyl-3,5-heptanedionato)calcium (hereinafterabbreviated to Ca(DPM)₂) represented by the following chemical formula:

Next, HAT(CN)₆ was formed into a film of 10 nm thickness as thehole-generating and transporting section 4-1-c, and thereon Al wasformed into a film of 150 nm thickness as a cathode thereon by vacuumdeposition.

Reference Example 2

In Reference Example 2, a display element was produced in the same wayas in Reference Example 1 except that, instead of the formation of theCa(DPM)₂ layer, the following was formed into a film of 3 nm thicknessas the intermediate layer 4-1-b in the connection layer:bis(dipivaloylmethanato)magnesium (Mg(acac)₂) represented by thefollowing chemical formula:

Reference Example 3

In Reference Example 3, a display element was produced in the same wayas in Reference Example 1 except that, instead of the formation of theCa(DPM)₂ layer, MgF₂ was formed into a film of 1.5 nm thickness as theintermediate layer 4-1-b in the connection layer.

Reference Example 4

In Reference Example 4, a display element was produced in the same wayas in Reference Example 1 except that, instead of the formation of theCa(DPM)₂ layer, AlF₃ was formed into a film of 3 nm thickness as theintermediate layer 4-1-b in the connection layer.

Evaluation:

After the film formation of each of the elements of Reference Examples 1to 4, the substrate was shifted into an inert glove box. A UV curableresin was applied onto a glass cap, and the substrate and the cap werebonded each other. This substrate was taken out into the atmosphere, anda voltage was applied to the element to evaluate a current-voltagerelationship. Shown are the comparison result of Reference Examples 1and 2 in FIG. 2; the comparison result of Reference Examples 1 and 3 inFIG. 3; and the comparison result of Reference Examples 1 and 4 in FIG.4. In each of these Reference Examples, four elements were producedsimilarly. The measurement results of the elements are shown in the samefigure. For the elements of Reference Examples 1 to 4, the voltage andthe luminance obtained when the current density was 10 mA/cm² are shownin Table 1.

TABLE 1 Current Applied Intermediate density voltage Luminance layer(mA/cm²) (V) (cd/m²) Reference Example 1 Ca(DPM)₂ 10 4.8 279 ReferenceExample 2 Mg(acac)₂ 10 4.7 280 Reference Example 3 MgF₂ 10 5.8 272Reference Example 4 AlF₃ 10 8.2 74

According to FIGS. 2 to 4, it was observed that in Reference Example 3wherein MgF₂ having a resistivity of 10¹⁴ Ω·cm or more and a dielectricconstant of 5.0 was formed as the intermediate layer, the drivingvoltage was raised compared to Reference Example 1 wherein Ca(DPM)₂layer was formed as the intermediate layer, and Reference Example 2wherein Mg(acac)₂ layer was formed. It was also observed that inReference Example 4 wherein AlF₃ having a resistivity of 10¹⁴ Ω·cm ormore and a dielectric constant of 6.0 was formed as the intermediatelayer, the driving voltage raised and further the luminance was lowered.

It is understood that in the case of using a substance having too largeresistivity or dielectric constant for the intermediate layer 4-1-b ofthe connection layer as in Reference Examples 3 and 4, an extra voltageis applied to the connection layer so that charges tend to remain easilyinside the connection layer. In the four elements produced in ReferenceExample 4, a large variation was generated in the current-voltagemeasurement. Thus, it is considered that a problem existed with thestate of the connection between LiF in the electron-generating andtransporting section and HAT(CN)₆ in the hole-generating andtransporting section.

On the other hand, the elements of Reference Examples 1 and 2 were eachsmaller in driving voltage than those of Reference Examples 3 and 4. Itis therefore considered that the connection between theelectron-generating and transporting section and the hole-generating andtransporting section was good, thereby forming a connection layerwherein the remaining charges was slight. When such a connection layerin which the remaining charges are slight is sandwiched between plurallight-emitting units, the connection layer can satisfactorily act as acharge-generating layer for injecting electrons toward the anode andinjecting holes toward the cathode.

In each of the Examples, Reference Examples and Comparative Examplesdescribed below, a bottom-type evaluation substrate was produced thathad a light-emitting region 2 mm×2 mm in size formed on a glasssubstrate on which a patterned ITO film (thickness: 150 nm) was formedas an anode. In each of the Examples, a stacked type EL element asdescribed with reference to FIG. 1 was produced. Stacked structures of alight-emitting unit 3-1 and a connection layer 4-1 in each of theExamples, Reference Examples and Comparative Examples are shown in Table2.

TABLE 2 Light-emitting unit 3-1 Connection layer 4-1 Hole- Hole- Light-Electron- Reaction injecting transporting emitting transporting 4-1-agenerating 4-1-b 4-1-c Cathode Example 1 HAT NPD Alq LiF Al CaDPM HATLiF Al Example 2 HAT NPD Alq ETL-1 Liq Al CaDPM HAT Liq Al Example 3 HATNPD Alq ETL-1 Liq Al CaDPM/HAT HAT Liq Al Example 4 HAT NPD Alq ETL-1Liq Al MgDPM HAT Liq Al Example 5 Mo/NPD NPD Alq LiF Al CaDPM Mo/NPD LiFAl Example 6 Mo/NPD NPD Alq Liq Al CaDPM Mo/NPD Liq Al Example 7 Mo NPDAlq Liq Al CaDPM Mo Liq Al Example 8 Mo NPD Alq Liq Al CaDPM/Mo Mo LiqAl Comparative HAT NPD Alq LiF Al — HAT LiF Al Example 1 Comparative HATNPD Alq Alq/Liq Al — HAT Alq/Liq Al Example 2 Comparative HAT NPD AlqETL-1 Liq Al — HAT Liq Al Example 3 Reference HAT NPD Alq — LiF AlExample 5 Reference HAT NPD Alq ETL-1 — Liq Al Example 6 ComparativeMo/NPD NPD Alq LiF Al — Mo/NPD LiF Al Example 4 Comparative Mo/NPD NPDAlq Liq Al — Mo/NPD Liq Al Example 5 Comparative Mo NPD Alq Liq Al — MoLiq Al Example 6 Reference Mo/NPD NPD Alq — LiF Al Example 7 ReferenceMo/NPD NPD Alq — Liq Al Example 8 Example 9 Mo NPD Alq LiF Al Alq Mo LiFAl Example 10 Mo NPD Alq LiF Al NPD Mo LiF Al Example 11 HAT NPD AlqETL-1 Liq Al NPD/HAT HAT Liq Al Example 12 HAT NPD Alq ETL-1 Liq AlAlq/HAT HAT Liq Al Comparative Mo NPD Alq LiF Al — Mo LiF Al Example 7Comparative Mo NPD Alq Liq Al — Mo Liq Al Example 8 Reference Mo NPD Alq— LiF Al Example 9 Reference Mo NPD Alq — Liq Al Example 10

In Table 2, the structure of the light-emitting unit 3-2 is omitted. Inthe table, the symbol “/” denotes a vapor co-deposited film (vapordeposition ratio is omitted). In the table, the abbreviations are asfollows:

HAT: HAT(CN)₆,

Mo: molybdenum trioxide (MoO₃),

NPD: α-NPD,

Alq: Alq₃,

CaDPM: Ca(DPM)₂, and

MgDPM: Mg(DPM)₂

Examples about the First Embodiment Example 1

On the anode ITO a hole-injecting layer, a hole-transporting layer and alight-emitting layer as a first light-emitting unit were successivelyformed. First, HAT(CN)₆ was formed into a film of 10 nm thickness as thehole-injecting layer by vacuum deposition (deposition rate: 0.5 to 0.8nm/sec).

Next, α-NPD was formed into a film of 50 nm thickness as thehole-transporting layer thereon by vacuum deposition (deposition rate:0.8 to 1.2 nm/sec). Next, Alq₃ was formed into a film of 70 nmthickness, as the light-emitting layer functioning also as anelectron-transporting layer, thereon by vacuum deposition (depositionrate: 2.9 to 3.1 nm/sec).

On the first light-emitting unit an electron-generating and transportingsection 4-1-a, a non-semiconductor substance containing layer 4-1-b anda hole-generating and transporting section 4-1-c as a connection layerwere successively formed. First, LiF was formed into a film of 1 nmthickness as the electron-generating and transporting section 4-1-a, andthen Al was formed into a film of 1 nm thickness, as a layer forgenerating a reducing reaction with the LiF layer, thereon. Ca(DPM)₂ wasthen formed into a film of 3 nm thickness, as the non-semiconductorsubstance containing layer 4-1-b, thereon (deposition rate: 0.5 nm/sec).

Next, HAT(CN)₆ was formed into a film of 10 nm thickness as thehole-generating and transporting section 4-1-c thereon.

On the connection layer a second light-emitting unit 3-2 composed of anα-NPD layer of 50 nm thickness as a hole-transporting layer and an Alq₃layer of 70 nm thickness as a light-emitting layer was formed. Thehole-transporting layer and the light-emitting layer in the secondlight-emitting unit were formed under the same conditions as those forthe individual layers in the first light-emitting unit. Furthermore, LiFand Al were successively formed into a film of 1 nm thickness and a filmof 150 nm thickness, respectively, as a cathode 5 on the secondlight-emitting unit by vacuum deposition.

Example 2

In the same way as in Example 1, on the anode ITO an HAT(CN)₆ layer as ahole-injecting layer and an α-NPD layer as a hole-transporting layerwere formed. Alq₃ was formed into a film of 50 nm thickness, as alight-emitting layer, thereon and then an electron-transporting materialETL-1 (aromatic compound-type electron-transporting material) wasfurther formed into a film of 10 nm thickness thereon to form a firstlight-emitting unit.

An (8-quinolinolato)lithium complex (hereinafter abbreviated to Liq)represented by the following chemical formula was then formed into afilm of 2.5 nm thickness as an electron-generating and transportingsection 4-1-a thereon, and then Al was formed into a film of 1.5 nmthickness, as a layer for generating a reducing reaction with the Liqlayer, thereon:

In the same way as in Example 1, a Ca(DPM)₂ layer as a non-semiconductorsubstance containing layer 4-1-b, and an HAT(CN)₆ layer as ahole-generating and transporting section 4-1-c were successively formedthereon to form a connection layer.

On the connection layer a second light-emitting unit composed of anα-NPD layer as a hole-transporting layer and an Alq₃ layer as alight-emitting layer was formed under the same conditions as those, forthe individual layers in the first light-emitting unit. The secondlight-emitting unit was formed. Furthermore, LiF and Al weresuccessively formed into a film of 1 nm thickness and a film of 150 nmthickness, respectively, as a cathode 5 on the second light-emittingunit by vacuum deposition. Furthermore, Liq and Al were successivelyformed into a film of 2.5 nm thickness and a film of 150 nm thickness,respectively, as a cathode 5 on the second light-emitting unit by vacuumdeposition.

Examples 3-1 to 3-5

In Examples 3, display elements were each produced in the same way as inExample 2 except that a vapor co-deposited film of Ca(DPM)₂ and HAT(CN)₆was formed into a thickness of 10 nm as the non-semiconductor substancecontaining layer 4-1-b in the connection layer. The content of Ca(DPM)₂to the total of Ca(DPM)₂ and HAT(CN)₆ in the vapor co-deposited film was80% by weight in Example 3-1; 67% by weight in Example 3-2; 50% byweight in Example 3-3; 33% by weight in Example 3-4; and 20% by weightin Example 3-5.

Example 4

In Example 4, a display element was produced in the same way as inExample 2 except that instead of the formation of the Ca(DPM)₂ layer,(2,2,6,6-tetramethyl-3,5-heptanedionato)magnesium (hereinafterabbreviated to Mg(DPM)₂) was formed into a film of 3 nm thickness as thenon-semiconductor substance containing layer 4-1-b in the connectionlayer.

Comparative Example 1

In Comparative Example 1, a display element was produced in the same wayas in Example 1 except that the non-semiconductor substance containinglayer 4-1-b in the connection layer was not formed.

Comparative Example 2

In Comparative Example 2, a display element which did not have thenon-semiconductor substance containing layer 4-1-b was produced in thesame way as in Comparative Example 1 except that, instead of theformation of the LiF film of 1 nm thickness as each of theelectron-generating and transporting section 4-1-a and the cathode, Alq₃and Liq were formed into a film of 10 nm by vapor co-deposition with aratio by film thickness of 1:3.

Comparative Example 3

In Comparative Example 3, a display element was produced in the same wayas in Example 2 except that the non-semiconductor substance containinglayer 4-1-b in the connection layer was not formed.

Reference Example 5

In Reference Example 5, in the steps of producing the display element ofExample 1, an element having a one-unit structure, which was not astacked structure, was produced by forming the cathode 5 directly ontothe light-emitting unit 3-1.

Reference Example 6

In Reference Example 6, in the steps of producing the display element ofExample 2, an element having a one-unit structure which was not astacked structure was produced by forming the cathode 5 directly ontothe light-emitting unit 3-1.

After the formation of each of the elements of the Examples andComparative Examples, the substrate was shifted into an inert glove box.A UV curable resin was applied onto a glass cap, and the substrate andthe cap were bonded onto each other. This substrate was taken out intothe atmosphere, and a voltage was applied to the element to measure theluminance with a luminance meter, thereby evaluating thecurrent-voltage-luminance property (I. V. L) thereof. For each of theelements, the voltage and the luminance obtained when the currentdensity was 30 mA/cm² are shown in Table 3.

TABLE 3 Current Applied Light-emitting density voltage efficiencyLuminance (mA/cm²) (V) (cd/A) (cd/m²) Example 1 30 11.9 5.6 1687Comparative 30 15.7 5.6 1669 Example 1 Reference 30 6.4 3.1 937 Example5 Example 2 30 9.3 5.3 1643 Example 3-1 30 10.5 6.0 1793 Example 3-2 3010.2 5.8 1736 Example 3-3 30 9.8 5.7 1722 Example 3-4 30 9.7 5.7 1741Example 3-5 30 9.8 5.5 1696 Example 4 30 9.7 4.7 1397 Comparative 3012.3 4.8 1447 Example 2 Comparative 30 10.3 4.6 1388 Example 3 Reference30 5.3 3.1 948 Example 6

The comparison result of Example 1 and Reference Example 5 is shown inFIG. 5; the comparison result of Example 2 and Reference Example 6 isshown in FIG. 6; the comparison result of Example 2 and ComparativeExample 3 is shown in FIG. 7; the comparison result of Example 3-4 andReference Example 6 is shown in FIG. 10; the comparison result ofComparative Example 3 and Reference Example 6 is shown in FIG. 11; andthe comparison result of Example 4 and Reference Example 6 is shown inFIG. 13. Moreover, the comparison result of Example 3-4, ReferenceExample 6 and Comparative Example 3 is shown in FIG. 12. FIGS. 5, 6 and10, (1), (2), and (3) show the voltage-to-current density, thelight-emitting efficiency, and the current efficiency, respectively.FIGS. 11(1) and (2) show the voltage-to-current density, and thelight-emitting efficiency, respectively. FIG. 12 shows the comparisonresult of the voltage-to-current densities of Example 3-4, ComparativeExample 3, and Reference Example 6.

When the element of Example 1 is compared with the element of ReferenceExample 5 which had only one light-emitting unit, it is understood that:Example 1 exhibited a voltage about two times that of Reference Example5 when the two had the same current density as illustrated in FIG. 5(1);and that as illustrated in FIG. 5(2), in Example 1, the light-emittingefficiency of Reference Example 5 was sustained. In other words, it isunderstood that in Example 1, the luminance was about two times higherthan that in Reference Example 5 without damaging the electric powerlight-emitting efficiency of Reference Example 5 and thus the connectionlayer between the light-emitting units functioned ideally. It is alsounderstood from FIGS. 6, 10 and 13 that the same results are observedwhen the elements of Examples 2, 3-4 and, 4, and Reference Example 6 arecompared with each other.

In contrast, according to FIGS. 11 and 12, when Reference Example 6 iscompared with Comparative Example 3, Comparative Example 3 showed avoltage exceeding twice that of Reference Example 6 in the region ofhigh current densities. It is understood from this matter that inComparative Example 3, which did not have the intermediate layer 4-1-b,the electric power light-emitting efficiency was damaged.

FIG. 8 shows the comparison result of the voltage-to-current densitiesof Examples 2, 3-1, 3-4, and 3-5. FIG. 9 shows the comparison result ofthe voltage-to-current densities of Examples 2 and 3-1 to 3-5 in theregion of high voltages (10 V or more). In Example 3-4, the amount ofCa(DPM)₂, which is a non-semiconductor substance, in the intermediatelayer 4-1-b was 33% by weight, and the value obtained by multiplying thefilm thickness (10 nm) of the intermediate layer by the content of thenon-semiconductor substance was 3 nm. The element of Example 3-4 had anintermediate layer with a thickness of 3 nm, and had the samevoltage-current property as the element of Example 2, which had thesingle layer of Ca(DPM)₂ (content 100% by weight). It is understood fromthis matter that even when the intermediate layer is a mixed layer, byadjusting the value obtained by multiplying the thickness of theintermediate layer by the content of the non-semiconductor substance, itis possible to obtain an element wherein its connection layer functionsas a charge-generating layer in the same manner as in an element ofwhich the intermediate layer is a single layer, and the same property isexhibited. Moreover, in Example 3-3, wherein the content of Ca(DPM)₂ inthe intermediate layer was 50% by weight, and in Example 3-5, whereinthe content of Ca(DPM)₂ was 25% by weight, the obtained elements had thesame voltage-current property as in Example 3-4.

On the other hand, as shown in Table 3, Example 3-1, wherein the contentof Ca(DPM)₂ was 80% by weight, and Example 3-2, wherein the content ofCa(DPM)₂ was 67% by weight, were higher in voltage than Example 2 andExample 3-4, and gave a driving voltage equivalent to that ofComparative Example 3, which did not have the intermediate layer 4-1-b.In contrast, as shown in Table 3, the elements of Examples 3-1 and 3-2were higher in light-emitting efficiency than the element of ComparativeExample 3. It is therefore stated that the elements of Examples 3-1 and3-2 can be made lower in driving voltage than the element of ComparativeExample 3 when these elements are made to emit light with the sameluminance. Lifetime test results of Example 1, Comparative Example 1 andReference Example 5 are shown in FIG. 14, and lifetime test results ofExample 2, Comparative Example 3 and Reference Example 6 are shown inFIG. 15. Each of the lifetime test results in FIGS. 14 and 15 shows achange with time in the relative luminance that was obtained by anormalization to the luminance of each of the elements at the initialtime (time: 0), which was regarded as 1 under a condition that thecurrent density was a constant value of 70 mA/cm². It is understood fromthe results that in Comparative Examples 1 and 3, which had noconnection layer, the initial-luminance deterioration thereof wasremarkable and the deterioration with time was also large.

In contrast, it is understood that for each of the elements of Examples1 and 2, the lifetime was improved in comparison with the elements ofComparative Examples 1 and 2. The elements of Examples 1 and 2deteriorated more speedily than those of Reference Examples 5 and 6;however, this was because in Examples 1 and 2, the elements were made toemit light at about two times the electric power of in ReferenceExamples 5 and 6, i.e., with about two times the luminance of thattherein, since the lifetime test was carried out with a constant currentdensity.

Example 5

In Example 5, a display element was produced in the same way as inExample 1 except that, instead of the forming HAT(CN)₆ layers for eachof the hole-injecting layer in the first light-emitting unit and thehole-generating and transporting section 4-1-c in the connection layer,molybdenum trioxide (MoO₃) and α-NPD were formed into a film of 10 nm byvapor co-deposition with a ratio by film thickness of 1:9.

Example 6

In Example 6, a display element was produced in the same way as inExample 5 except that instead of forming a LiF film of 1 nm thicknessfor each of the electron-generating and transporting section 4-1-a andthe cathode, a Liq film of 1 nm thickness was formed.

Example 7

In Example 7, a display element was produced in the same way as inExample 6 except that, instead of forming a vapor co-deposited film ofMoO₃ and α-NPD for each of the hole-injecting layer in the firstlight-emitting unit and the hole-generating and transporting section4-1-c in the connection layer, a single layer of MoO₃ of 10 nm filmthickness was formed (deposition rate: 0.3 to 0.5 nm/sec).

Example 8

In Example 8, a display element was produced in the same way as inExample 7 except that Ca(DPM)₂ and MoO₃ were formed into a film of 2 nm,as the non-semiconductor substance containing layer 4-1-b in theconnection layer, by vapor co-deposition with a ratio of film thicknessof 1:1.

Comparative Example 4

In Comparative Example 4, a display element was produced in the same wayas in Example 5 except that the non-semiconductor substance containinglayer 4-1-b in the connection layer was not formed.

Comparative Example 5

In Comparative Example 5, a display element was produced in the same wayas in Example 6 except that the non-semiconductor substance containinglayer 4-1-b in the connection layer was not formed.

Comparative Example 6

In Comparative Example 6, a display element was produced in the same wayas in Example 7 except that the non-semiconductor substance containinglayer 4-1-b in the connection layer was not formed.

Reference Example 7

In Reference Example 7, in the steps of producing the display element ofExample 5, an element having a one-unit structure which was not astacked structure was produced by forming the cathode 5 directly ontothe light-emitting unit 3-1.

Reference Example 8

In Reference Example 8, in the steps of producing the display element ofExample 6, an element having a one-unit structure which was not astacked structure was produced by forming the cathode 5 directly ontothe light-emitting unit 3-1.

After the formation of each of the elements of the Examples andComparative Examples, the substrate was shifted into an inert glove boxunder inert conditions. A UV curable resin was applied onto a glass cap,and the substrate and the cap were bonded onto each other. Thissubstrate was taken out into the atmosphere, and a voltage was appliedto the element to evaluate the current-voltage relationship. The resultsare shown in Table 4. The comparison result of Example 5, ComparativeExample 4 and Reference Example 7 is shown in FIG. 16; and thecomparison result of Example 6, Comparative. Example 5 and ReferenceExample 8 is shown in FIG. 17. FIGS. 16 and 17, (1) and (2) show thevoltage-to-current density, and the light-emitting efficiency,respectively.

TABLE 4 Current Applied Light-emitting density voltage efficiencyLuminance (mA/cm²) (V) (cd/A) (cd/m²) Example 5 30 13.4 5.1 1547Comparative 30 14.7 5.0 1543 Example 4 Reference 30 6.1 3.4 1045 Example7 Example 6 30 11.4 5.0 1574 Comparative 30 11.5 5.0 1488 Example 5Reference 30 5.9 3.4 1114 Example 8

When the element of Example 5 is compared with the element of ReferenceExample 7, which had only one light-emitting unit, it is understoodthat: Example 5 exhibited about two times the voltage of that ofReference Example 7 when the two had the same current density as shownin FIG. 16(1) and Table 4; and that from FIG. 16(2) the element ofExample 5 had a high current efficiency. By contrast, ComparativeExample 4 exhibited a voltage exceeding two times the voltage of that ofReference Example 7 when these had the same current density; thus, it isunderstood that the current efficiency lowered remarkably in the regionof high luminances. In other words, it is understood that in Example 5,the luminance was about two times higher than that in Reference Example7 without damaging the electric power light-emitting efficiency ofReference Example 7 and thus the connection layer between thelight-emitting units functioned ideally.

When Example 6, Comparative Example 5, and Reference Example 8 arecompared with each other, the same tendency is recognized. However, itis understood that the comparison between Example 5 wherein LiF was usedfor the electron-generating and transporting section 4-1-a, andComparative Example 4 demonstrates a more remarkable difference based onwhether or not these elements each had the layer containing theelectrically insulating non-semiconductor substance. From this matter,it is understood that in a structure wherein LiF is used for anelectron-generating and transporting section of a lining layer, thepresence of the non-semiconductor substance containing layer 4-1-b isparticularly important.

Examples about the Second Embodiment Example 9

On the anode ITO a hole-injecting layer, a hole-transporting layer and alight-emitting layer as a first light-emitting unit were successivelyformed. First, MoO₃ was formed into a film of 10 nm thickness as thehole-injecting layer by vacuum deposition (deposition rate: 0.3 to 0.5nm/sec). Next, α-NPD was formed into a film of 50 nm thickness as thehole-transporting layer thereon by vacuum deposition (deposition rate:0.8 to 1.2 nm/sec). Next, Alq₃ was formed into a film of 60 nmthickness, as the light-emitting layer functioning also as anelectron-transporting layer, thereon by vacuum deposition (depositionrate: 2.9 to 3.1 nm/sec).

On the first light-emitting layer 3-1 an electron-generating andtransporting section 4-1-a, an electron-transporting organic materialcontaining layer 4-1-b, and a hole-generating and transporting section4-1-c as a connection layer were successively formed.

First, LiF was formed into a film of 1 nm thickness as theelectron-generating and transporting section 4-1-a, and then Al wasformed into a film of 1 nm thickness, as a layer for generating areducing reaction with the LiF layer, thereon. Alq₃, which is anelectron-transporting organic material, was then formed into a film of 2nm thickness, as the electron-transporting organic material containinglayer 4-1-b, thereon (deposition rate: 0.5 nm/sec).

Next, MoO₃ was formed into a film of 10 nm thickness as thehole-generating and transporting section 4-1-c thereon.

On the connection layer a second light-emitting unit composed of a MiO₃layer of 10 nm thickness as a hole-transporting layer and an Alq₃ layerof 60 nm thickness as a light-emitting layer was formed. Thehole-transporting layer and the light-emitting layer in the secondlight-emitting unit were formed under the same conditions as used toform the individual layers in the first light-emitting unit.Furthermore, LiF and Al were formed into a film of 1 nm thickness and afilm of 150 nm thickness, respectively, as a cathode 5 on the secondlight-emitting unit by vacuum deposition.

Example 10

In Example 10, a display element was produced in the same way as inExample 9 except that, instead of the formation of Alq₃, the film of theelectron-transporting organic material as the charge-transportingorganic material containing layer 4-1-b in the connection layer, α-NPD,which is a hole-transporting organic material, was formed into a film of2 nm thickness (deposition rate: 0.5 nm/sec).

Comparative Example 7

In Comparative Example 7, a display element was produced in the same wayas in Example 9 except that the charge-transporting organic materialcontaining layer 4-1-b in the connection layer was not formed.

Comparative Example 8

In Comparative Example 8, a display element was produced in the same wayas in Example 9 except that instead of the formation of the LiF film of1 nm thickness for each of the electron-generating and transportingsection 4-1-a and the cathode, Liq was formed into a film of 1 nmthickness, and the intermediate layer 4-1-b was not formed.

Reference Example 9

In Reference Example 9, in the steps of producing the display element ofExample 9, an element having a one-unit structure which was not astacked structure was produced by forming the cathode 5 directly ontothe light-emitting unit 3-1.

Reference Example 10

Reference Example 10, in the steps of producing the display element ofComparative Example 8, an element having a one-unit structure which wasnot a stacked structure was produced by forming the cathode 5 directlyonto the light-emitting unit 3-1.

After the formation of each of the organic EL elements of Examples 9 and10, Comparative Examples 7 and 8, and Reference Examples 9 and 10 eachproduced as described above, the substrate was shifted into an inertglove box. A UV curable resin was applied onto a glass cap, and thesubstrate and the cap were bonded onto each other. This substrate wastaken out into the atmosphere, and a voltage was applied to the elementto measure the luminance with a luminance meter, thereby evaluating avoltage-current-luminance property (I. V. L). In Table 5 the voltage andthe luminance of each of the elements that were generated when thecurrent density was 30 mA/cm² are shown.

TABLE 5 Current Applied Light-emitting density voltage efficiencyLuminance (mA/cm²) (V) (cd/A) (cd/m²) Example 9 30 13.1 5.1 1608 Example10 30 12.3 4.7 1435 Comparative 30 15.3 3.4 1041 Example 7 Reference 306.1 3.3 986 Example 9 Comparative 30 12.1 4.9 1518 Example 8 Reference30 6.1 3.3 986 Example 10

As also understood from Table 5, the elements of Examples 9 and 10 werelower in driving voltage than the organic EL element of ComparativeExample 7 when these elements had the same current density. Thus, it isunderstood that in the elements of Examples 9 and 10, an extra voltagegenerated when plural light-emitting units were laminated was decreased.

In FIG. 18, lifetime test results of the elements of Examples 9 and 10,Comparative Example 8 and Reference Example 10 are shown. The lifetimetest results in FIG. 18 each show a change with time in the relativeluminance that was obtained by a normalization to the luminance of theelement at the initial time (time: 0), which was regarded as 1 under acondition that the current density was a constant value of 70 mA/cm². Itis understood from the results that the elements of Examples 9 and 10were better improved in element lifetime than the element of ComparativeExample 8 so as to be comparable to the element of Reference Example 10which had only one light-emitting unit.

Example 11

In Example 11, a display element was produced in the same way as inExample 2 except that a vapor co-deposited film of α-NPD and HAT(CN)₆(ratio by weight of 1:1) was formed into a film thickness of 10 nm(deposition rate: 0.5 to 0.8 nm/sec) as the intermediate layer 4-1-b inthe connection layer.

Example 12

In Example 12, a display element was produced in the same way as inExample 2 except that a vapor co-deposited film of Alq₃ and HAT(CN)₆(ratio by weight of 1:2) was formed into a film thickness of 10 nm asthe intermediate layer 4-1-b in the connection layer.

After the formation of each of the organic EL elements of Examples 11and 12 each produced as described above, the substrate was shifted intoan inert glove box. A UV curable resin was applied onto a glass cap, andthe substrate and the cap were bonded onto each other. This substratewas taken out into the atmosphere, and a voltage was applied to theelement to measure the luminance with a luminance meter, therebyevaluating the voltage-current-luminance property (I. V. L). For each ofthe elements of Examples 11 and 12, the voltage and the luminancegenerated when the current density was 30 mA/cm², together with theresults of Comparative Examples 1 and 3 are shown in Table 6.

TABLE 6 Current Applied Light-emitting density voltage efficiencyLuminance (mA/cm²) (V) (cd/A) (cd/m²) Example 11 30 10.2 5.6 1778Comparative 30 15.7 5.6 1669 Example 1 Example 12 30 10.0 5.4 1644Comparative 30 10.3 4.6 1388 Example 3

As also understood from Table 6, the elements of Examples 11 and 12where the charge-transporting organic material containing layer wasformed as the intermediate layer 4-1-b, were lower in driving voltagethan Comparative Examples 1 and 3 which each had no connection layer,when these elements had the same current density. Thus, it is understoodthat, in the elements of Examples 11 and 12, an extra voltage generatedwhen the plural light-emitting units were laminated was decreased.

As shown above through the comparisons of Examples, Comparative Examplesand Reference Examples of the first embodiment of the invention, whichhas a layer containing an electrically-insulating non-semiconductorsubstance as the intermediate layer 4-1-b of the connection layer, andthe second embodiment of the invention, which has a layer containing acharge-transporting organic material as its intermediate layer 4-1-b,the connection layer acts satisfactorily as a charge-generating layer.Thus, it is understood that the voltage-rise in the case of laminatingthe plural light-emitting units is restrained so that the lifetime ofthe element can be extended.

DESCRIPTION OF REFERENCE CHARACTERS

-   -   1 substrate    -   2 anode    -   3-1 and 3-2 light-emitting units    -   4-1 connection layer    -   4-1-a electron-generating and transporting section    -   4-1-b intermediate layer    -   4-1-c hole-generating and transporting section    -   5 cathode

1. An organic electroluminescent element, comprising an anode, acathode, plural light-emitting units that are stacked between the anodeand the cathode, each light-emitting unit comprising at least oneorganic light-emitting layer, and a connection layer sandwiched betweenthe respective light-emitting units, wherein in the connection layer,the following are successively stacked from the anode side: anelectron-generating and transporting section comprising at least oneselected from the group consisting of alkali metals, alkaline earthmetals, rare earth metals, and alloys of these metals, and compounds ofthese metals; a layer comprising a non-semiconductor substance having aresistivity of 1.0×10² to 1.0×10⁹ Ω·cm; and a hole-generating andtransporting section.
 2. The organic electroluminescent elementaccording to claim 1, wherein the non-semiconductor substance which iselectrically insulating has a dielectric constant of 2 to 4.5 inclusive.3. The organic electroluminescent element according to claim 1, whereinthe hole-generating and transporting section comprises anazatriphenylene derivative represented by the following general formula(I):

wherein R1 to R6 are each independently selected from the groupconsisting of hydrogen, nitrile, nitro, sulfonyl, sulfoxides,trifluoromethyl, esters, amides, substituted or unsubstituted aryls,substituted or unsubstituted heteroaryls, and substituted orunsubstituted alkyls; and any adjacent Rn's wherein n represents 1 to 6may be bonded to each other through a cyclic structure.
 4. The organicelectroluminescent element according to claim 1, wherein the layercomprising the non-semiconductor substance is a mixed layer comprisingthe non-semiconductor substance, and an azatriphenylene derivativerepresented by the following general formula (I):

wherein R1 to R6 are each independently selected from hydrogen, nitrile,nitro, sulfonyl, sulfoxides, trifluoromethyl, esters, amides,substituted or unsubstituted aryls, substituted or unsubstitutedheteroaryls, and substituted or unsubstituted alkyls; and any adjacentRn's wherein n represents 1 to 6 may be bonded to each other through acyclic structure.
 5. The organic electroluminescent element according toclaim 4, wherein a content of the non-semiconductor substance in themixed layer is 10% or more by weight.
 6. The organic electroluminescentelement according to claim 1, wherein the hole-generating andtransporting section comprises a metal oxide having a hole-injectingability.
 7. The organic electroluminescent element according to claim 6,wherein the metal oxide comprises at least one selected from the groupconsisting of molybdenum oxide, ruthenium oxide, manganese oxide,tungsten oxide, and vanadium oxide.
 8. The organic electroluminescentelement according to claim 6, wherein the layer comprising thenon-semiconductor substance is a mixed layer comprising thenon-semiconductor substance and the metal oxide having a hole-injectingability.
 9. The organic electroluminescent element according to claim 8,wherein a content of the non-semiconductor substance in the mixed layeris 10% or more by weight, and further the mixed layer comprises 10% ormore by weight of molybdenum trioxide as the metal oxide having thehole-injecting ability.
 10. The organic electroluminescent elementaccording to claim 6, wherein the hole-generating and transportingsection is a mixed layer of the metal oxide having a hole-injectingability, and a hole-transporting material.
 11. The organicelectroluminescent element according to claim 10, wherein thehole-transporting material is an arylamine compound.
 12. An organicelectroluminescent element, comprising an anode, a cathode, plurallight-emitting units that are stacked between the anode and the cathode,each light-emitting unit comprising at least one organic light-emittinglayer, and a connection layer sandwiched between the respectivelight-emitting units, wherein in the connection layer, the following aresuccessively stacked from the anode side: an electron-generating andtransporting section comprising at least one selected from the groupconsisting of alkali metals, alkaline earth metals, rare earth metals,and alloys of these metals, and compounds of these metals; a layercomprising a charge-transporting organic material; and a hole-generatingand transporting section.
 13. The organic electroluminescent elementaccording to claim 12, wherein the hole-generating and transportingsection comprises an azatriphenylene derivative represented by thefollowing general formula (I):

wherein R1 to R6 are each independently selected from the groupconsisting of hydrogen, nitrile, nitro, sulfonyl, sulfoxides,trifluoromethyl, esters, amides, substituted or unsubstituted aryls,substituted or unsubstituted heteroaryls, and substituted orunsubstituted alkyls; and any adjacent Rn's wherein n represents 1 to 6may be bonded to each other through a cyclic structure.
 14. The organicelectroluminescent element according to claim 12, wherein the layercomprising the charge-transporting organic material is a mixed layer ofan azatriphenylene derivative represented by the following generalformula (I), and the charge-transporting organic material:

wherein R1 to R6 are each independently selected from the groupconsisting of hydrogen, nitrile, nitro, sulfonyl, sulfoxides,trifluoromethyl, esters, amides, substituted or unsubstituted aryls,substituted or unsubstituted heteroaryls, and substituted orunsubstituted alkyls; and any adjacent Rn's wherein n represents 1 to 6may be bonded to each other through a cyclic structure.
 15. The organicelectroluminescent element according to claim 12, wherein thehole-generating and transporting section is a metal oxide layer having ahole-injecting ability.
 16. The organic electroluminescent elementaccording to claim 15, wherein a metal oxide which forms the metal oxidelayer having the hole-injecting ability comprises at least one selectedfrom the group consisting of molybdenum oxide, ruthenium oxide,manganese oxide, tungsten oxide, and vanadium oxide.
 17. The organicelectroluminescent element according to claim 15, wherein the layercomprising the charge-transporting organic material is a mixed layercomprising the charge-transporting organic material, and a metal oxide.18. A display device, comprising an organic electroluminescent elementaccording to claim
 1. 19. A lighting apparatus, comprising an organicelectroluminescent element according to claim 1.